Wednesday, January 03, 2018

Old forests are essential to sequestering carbon, logging doubles release

(Burning wood is not carbon neutral.)

From The Hidden Life of Trees by Peter Wohlleben, ch. 16:

In a very simple, widely circulated image of natural cycles, trees are poster children for a balanced system. As the photosynthesize, they produce hydrocarbons, which fuel their growth, and over the course of their lives, they store up to 22 tons of carbon dioxide in their trunks, branches, and root systems. When they die, the same exact quantity of greenhouse gases is released a s fungi and bacteria break down the wood, process the carbon dioxide, and breath it out again. The assertion that burning wood is climate neutral is based on this concept. After all, it makes no difference if it’s small organisms reducing pieces of wood to their gaseous components or if the home hearth takes on this task, right? But how a forest works is way more complicated than that. The forest is really a gigantic carbon dioxide vacuum that constantly filters out and stores this component of the air.

It’s true that some of this carbon dioxide does indeed return to the atmosphere after a tree’s death, but most of it remains locked in the ecosystem forever. The crumbling trunk is gradually gnawed nad munched into smaller and smaller pieces and worked, by fractions of inches, more deeply into the soil. The rain takes care of whatever is left, as it flushes organic remnants down into the soil. The farther underground, the cooler it is. And as the temperature falls, life slows down, until it comes almost to a standstill. Adn so it is that carbon dioxide finds its final resting place in the form of humus, which continues to become more concentrated as it ages. ...

Today, ... forests are constantly being cleared, thanks to modern forest management practices (aka logging). As a result, warming rays of sunlight reach the ground and help the species living there kick into high gear. This means they consume humus layers even deep down into the soil, releasing the carbon they contain into the atmosphere as gas. The total quantity of climate-changing gases that escapes is roughly equivalent to the amount of timber that has been felled. For every log you burn in your fire at home, a similar amount of carbon dioxide is being released from the forest floor outside. And so carbon stores in the ground below trees in our latitudes are being depleted as fast as they are being formed. ...

Where is the end of the road for our forests? Will they go on storing carbon until someday there isn’t any left in the air? This, by the way, is no longer a question in search of an answer, thanks to our consumer society, for we have already reversed the trend as we happily empty out the earth’s carbon reservoirs. We are burning oil, gas, and coal as heating materials and fuel, and spewing their carbon reserves out into the air. In terms of climate change, could it perhaps be a blessing that we are liberating greenhouse gases from their underground prisons and setting them free once again? Ah, not so fast. True, there has been a measurable fertilizing effect as the levels of carbon dioxide in the atmosphere have risen. The latest forest inventories document that trees are growing more quickly than they used to. The spreadsheets that estimate lumber production need to be adjusted now that one third more biomass is accruing than a few decades ago. But what was that again? If you are a tree, slow growth is the key to growing old. ... And so the tried and tested rule holds true: less (carbon dioxide) is more (life-span).

When I was a student of forestry, I learned that young trees are more vigorous and grow more quickly than old ones. The doctrine holds to this day, with the result that forests are constantly being rejuvenated. Rejuvenated? That simply means that all the old trees are felled and replaced with newly planted little trees. Only then, according to the current pronouncements of associations of forest owners and representatives of commercial forestry, are forests stable enough to produce adequate amounts of timber to capture carbon dioxide out of the atmosphere and store it. Depending on what tree you are talking about, energy for growth begins to wane from 60 to 120 years of age, and that means it is time to roll out the harvesting machines. Has the ideal of eternal youth, which leads to heated discussions in human society, simply been transferred to the forest? It certainly looks that way, for at 120 years of age, a tree, considered from a human perspective, has barely outgrown its school days.

In fact, past scientific assumptions in this area appear to have gotten ahold of the completely wrong end of the stick, as suggested by a study undertaken by an international team of scientists. The researchers looked at about 700,000 trees on every continent around the world. The surprising result: the older the tree, the more quickly it grows. Trees with trunks 3 feet in diameter generated three times as much biomass as trees that were only half as wide. So, in the case of trees, being old doesn’t mean being weak, bowed, and fragile. Quite the opposite, it means being full of energy and highly productive. This means elders are markedly more productive than young whippersnappers, and when it comes to climate change, they are important allies for human beings. Since the publication of this study, the exhortation to rejuvenate forests to revitalize them should at the very least be flagged as misleading. The most that can be said is that as far as marketable lumber is concerned, trees become less valuable after a certain age. In older trees, fungi can lead to rot inside the trunk, but this doesn’t slow future growth one little bit. If we want to use forests as a weapon in the fight against climate change, then we must allow them to grow old ....